Currently, efforts are underway to integrate radio frequency transmission of isochronous data and asynchronous data. Recent changes to rules of the Federal Communications Commission in the United States have prompted these efforts. Similarly, the commercial need to communicate both voice information and data has prompted the search for efficient methods of communication.
Isochronous data is data which is continuously, periodically transmitted and of indeterminate, potentially continuous duration. An isochronous data source outputs data in a continuous data stream, usually at a substantially constant average data rate, possibly in packets or segments of data. Examples include video camera output and telephone voice output. These can be sources of a substantially continuous output of voice data, either analog or digitized. Isochronous data is generally real time data, and must be transmitted either continuously or periodically at uniform duration and period.
Asynchronous data is data which is packetized and is organized in discrete blocks of finite duration. The amount and duration of transmitted asynchronous data is generally variable and unpredictable. An asynchronous data source outputs data randomly or periodically, in variable size blocks or in constant size blocks. Examples include a computer workstation or laptop computer. Asynchronous data is optimally transmitted in contiguous blocks which may readily be stored or buffered for an indeterminate time before or after transmission.
In the United States, the Federal Communications Commission has defined unlicensed spectrum for communication of isochronous data and asynchronous data. The 1910 MHz-1920 MHz and 2390 MHz-2400 MHz bands are reserved for use by asynchronous devices. The 1920 MHz-1930 MHz band is reserved for use by isochronous devices.
However, the differing nature of isochronous data and asynchronous data has to date limited the integrated transmission of both types of data. Protocols which have been developed for communication of one data type do not efficiently communicate both data types.
For example, time division, multiple access (TDMA) communication systems have been developed for communication of voice data. In such systems, communication occurs on one or more frequencies during frames consisting of repeated time slots of uniform time duration and spacing. Each communication unit in the system is assigned a time slot for transmission and reception of digitized voice information. The units all operate synchronously. Examples of such systems are digital cellular telephone systems according to EIA/TIA standards IS-54 and IS-136.
Many such systems make provision for transmission of data other than voice data in assigned time slots. However, because frame definition and time slot duration are uniform, the system is insufficiently flexible to accommodate the variable and unpredictable nature of asynchronous data. Asynchronous data must be transmitted using the uniform-duration time slots and synchronous protocol, which is slow and inefficient. Because the isochronous voice data is real time, transmission of isochronous data cannot be interrupted beyond the predefined time slotting of the voice channel to permit efficient transmission of asynchronous data. Conventional systems lack the ability to efficiently communicate both asynchronous data and isochronous data.
Accordingly, there is a need in the art for an apparatus and method for integrated RF communication of asynchronous data and isochronous data such as voice information.